docs: def get_template_from_request(request, page=None):
      """
      Gets a valid template from different sources or falls back to the
      default template.
      """
      page_templates = settings.get_page_templates()
      if len(page_templates) == 0:
          return settings.PAGE_DEFAULT_TEMPLATE
      template = request.POST.get('template', request.GET.get('template', None))
      if template is not None and \
              (template in list(dict(page_templates).keys()) or
              template == settings.PAGE_DEFAULT_TEMPLATE):
          return template
      if page is not None:
          return page.get_template()
      return settings.PAGE_DEFAULT_TEMPLATE